1. Field of the Invention
The present invention relates to a system, such as a home theater system, which processes video signals and audio signals to be synchronized and reproduced, an apparatus used in the system, and a method of synchronizing video and audio used in the system.
2. Description of the Related Art
Many pieces of digital content of, for example, movies recorded on digital versatile disks (DVDs) have been provided. Home theater systems are increasingly used so that users can enjoy high-quality video and audio of such digital content at home. Such a home theater system includes, for example, a video and audio signal reproducing apparatus 1, such as a DVD player, an audio output apparatus 2, such as an audio amplifier, and a video display apparatus 3, such as a TV monitor (TV set).
The video and audio signal reproducing apparatus 1 reads out video signals and audio signals of digital content of, for example, movies recorded on recording media, such as DVDs, and outputs the readout video and audio signals.
The audio output apparatus 2 generates audio signals to be supplied to a speaker from the audio signals supplied from the video and audio signal reproducing apparatus 1 and supplies the generated audio signals to the speaker. The audio signals may be a multi-channel signal, such as a 2-channel signal, a 4-channel signal, or a 5.1-channel signal.
The video display apparatus 3 generates video signals to be supplied to a display unit where video is displayed from the video signals supplied from the video and audio signal reproducing apparatus 1. Video signals by various scanning methods using various numbers of scanning lines are supplied to the video display apparatus 3. The scanning methods include 480p (progressive scanning (sequential scanning) using 480 effective scanning lines), 720p (progressive scanning using 720 effective scanning lines), and 1080i (interlaced scanning using 1,080 effective scanning lines). In other words, the video signals to be reproduced have various formats.
Since the video signals and the audio signals supplied from the video and audio signal reproducing apparatus 1 are processed in the different apparatuses, as described above, it takes different times to process the audio and video signals. Generally, the processing of the video signals takes more time than the processing of the audio signals because a larger amount of data is processed for the video signals. Accordingly, any delay (delay in lip synchronization) can be caused between the audio output from the speaker and the video displayed in the display unit and, thus, viewers (users) who view digital content that is played back can feel discomfort.
Consequently, if the video and audio signal reproducing apparatus 1, the video display apparatus 3, and the audio output apparatus 2 are sequentially connected to each other in this order as shown in FIG. 1A, detecting a time necessary to process the video signals in the video display apparatus 3 and delaying the output of the audio signals to be transmitted to the video display apparatus 3 in accordance with the detected time allow synchronization (lip synchronization) between the time when the video is displayed in the video display apparatus 3 and the time when the audio is output in the audio output apparatus 2.
However, in many home theater systems, the video and audio signal reproducing apparatus 1, the audio output apparatus 2, and the video display apparatus 3 are sequentially connected to each other in this order, as shown in FIG. 1B. In this case, since the audio output apparatus 2 does not know the time during which the video signals are processed in the video display apparatus 3, the video can be out of synchronization with the audio.
Accordingly, Japanese Unexamined Patent Application Publication No. 2006-33436 discloses a technology in which the audio output apparatus 2 is connected to the video display apparatus 3 also via a control line ct, as shown in FIG. 1C. In this technology, the audio output apparatus 2 acquires information concerning the processing times of the video signals having different formats from a memory in the video display apparatus 3 through the control line ct and delays the audio signals to be output in accordance with the formats of the video signals which the audio output apparatus 2 has received and which is supplied from the audio output apparatus 2 to the video display apparatus 3.
With the technology disclosed in Japanese Unexamined Patent Application Publication No. 2006-33436, the audio output apparatus 2 can control the delay of the audio signals in accordance with the formats of the video signals which are supplied from the audio output apparatus 2 to the video display apparatus 3 by acquiring the processing times of the video signals having different formats from the video display apparatus 3, for example, when the audio output apparatus 2 is turned on. In other words, it is possible to eliminate the delay (the delay in the lip synchronization) between the reproduced video and the reproduced audio, caused by the video display apparatus 3 that processes the video signals having different formats.